Their island in the sun. St. Helena Island, S.C., is held in a special unwritten trust of family and church ties

COBWEBS of Spanish moss drape the mighty arms of great live oaks. But the trees are no older than the families of this sea island, descendants of slaves who toiled on cotton and rice plantations here before the Civil War. ``I'm proud of it - to be here and own my own land, my own home,'' declares Lucile Brown, who lives with four generations of her family on land distributed to freed slaves after the war.

For more than a century, black families have farmed and fished along the coast of South Carolina and Georgia, cut off from the world by marshland and segregation. The land gave them the resources to be self-sufficient, economically independent, truly free.

But along with greater job opportunities, modern times have brought an influx of wealthy vacationers. Islands from South Carolina to Florida have been sculpted into exclusive private resorts. Land prices - and taxes - are soaring. And in the last 30 years the islands' black population has dropped by half, to a little more than 100,000.

``It's very important for you to stay on your land. If you don't, someone is sure to get it,'' warns Mrs. Brown, a 75-year-old woman with a kind, worn face. ``If you let it go, you can't get it back.

``People on this plantation are lucky,'' she continues, looking from her porch across her family's homes and fields. ``They go away, but then they come back home.''

Bridges have connected St. Helena with the city of Beaufort since the 1920s and to the luxurious resorts on Fripp, Harbor, and Dataw Islands since the 1960s and '70s.

But the rural communities here have been only lightly touched by time.

The islanders' Gullah language and habits of culture have changed so little in centuries that they can still be traced to the African nation of Sierra Leone.

On the 45 square miles of the island, there are no incorporated towns. Communities, self-governing, are bound by churches and family ties.

Developers see St. Helena's quiet forests and shores as ``unused land,'' ripe for change. But to the islanders, the land is held in unwritten trust - for the family, not for sale.

``I would like to hold on to every piece of property that we own, because you have children, and children's children, and they have to have a place to stay,'' says Jonathan Mack, 57, who lives across Seaside Road from Lucile Brown.

Like three-quarters of St. Helena's 6,200 residents, Mr. Mack is living on ``heirs' property'' - land passed down through his family for more than 100 years. Within a quarter mile of Mack's brick house live the families of his brother Edward, his uncles Thomas and Joseph, his oldest son Jonathan Jr., and his nephews Joseph Jr. and Walter. All are living on the Mack family land.

``I don't believe in selling unless they're somebody that doesn't have a place to stay,'' says Mack, working on his tractor in his backyard, beside a small boat, a pen of chickens, and a young pig. ``I'd rather give them some land. I don't believe in selling land.''

This pattern of heirs' ownership has fostered a vast network of family ties. ``On Fripp Plantation, one or two of us is not related, as far as I know,'' says Mack, referring to about 100 neighbors who live on the historical Fripp Plan-tation land.

In the close community, grandmothers and grandchildren mingle as casually as fathers and sons. Today Lucile Brown's son James drops by her kitchen for a chat, while another son, Anthony, clears bushes in her yard. As Mrs. Brown talks, she keeps an eye on her great-grandchildren, La Toya, 7, and Tony, 3.

``Their mother went to work this morning, and her mother went away, so she asked me to keep them,'' Brown says matter-of-factly of the children. They are playing in her living room, cluttered with photographs of two dozen relatives in graduation caps and gowns.

Jonathan Mack and Jonathan Jr. are splitting firewood today. They talk as they work of how to repair an engine.

``If you need something, there is always someone you can go to,'' says Mr. Mack's youngest son, Kevin, 16. Two of his favorite relatives are his grandmother and his Aunt Claudia, who helped to raise him. ``They're just good to be around,'' Kevin says.

Skills for working on the land are passed down through the generations. In the flat soil dotted with shells, families plant collards and turnips, sweet potatoes and corn.

Kevin, in most ways a typical teenager who likes to play basketball and ride his motorcycle, is off this Saturday morning to his job at LeRoy Brown's farm. He will make potato hotbeds, a skill he learned from his father.

Islanders like Ernest Coleman, son of an island fisherman, catch crabs and shrimps in the creeks that wind slowly through the marsh. ``It's a simple business, but good,'' says Mr. Coleman, shaking a few blue crabs into his boat as pelicans and gulls watch from above.

From crabbing and shrimping, Coleman has earned enough to build a house and send four children to college, he reports with visible pride. ``Me and him going into business as soon as I get older,'' volunteers his 15-year-old son, John, who is helping to sort the crabs into wooden crates.

Other islanders hunt deer and squirrels that thrive in the tangled forests of wisteria, palms, and loblolly pine.

But the traditional self-sufficiency of families has lessened, as most young people have found work off the island.

Lucile Brown's sons, James and Anthony, and Jonathan Mack's son Clarence work at the Marine Corps bases on Parris Island and Beaufort. Mrs. Brown's daughter is a cook at a golf course on Fripp Island. Kevin hopes to work someday managing a store. And Jonathan Jr., with a degree in biology from Voorhees College in Denmark, S.C., is working as a brickmason.

``If you doesn't have a job now, it's sort of hard to make a living,'' says Jonathan Mack Sr., noting the modern struggle of small farmers to survive. Times have changed since he was a boy, he says, recalling the self-sufficiency of his grandfather's farm.

``Families were much closer back then because they had be together just to live,'' says Dorothy, Jonathan Jr.'s wife, born in the community of Scott Plantation seven miles down the road. ``Now everyone is working, doing their own separate things.''

On scattered lots around the island, ``For Sale'' signs bear witness to the land's loosening ties. A group of about 60 vacation homes clusters along the shore at Land's End Road.

``It's a little different from the past when everyone wanted to keep all the land in the family,'' comments Dorothy with a sigh. ``Now some of them sell it for money, not thinking about the purpose of having something that their ancestors had.''

But on Fripp Plantation, as elsewhere on St. Helena, young people who have gone away to college or to work are coming back, building houses and settling on their family land. With each return, the obligation to hold the land for future generations carries forward.

``The land my father gave me, I'd like to keep it in the family,'' says Jonathan Jr. ``I'd like to pass it on to my daughter.'' Dorothy agrees: ``Family is still the most important thing.''

For those who want to stay, the struggle is to fight rising taxes. But islanders here have learned from development nearby. At St. Helena's nonprofit Penn School, which promotes the history, culture, and economic survival of blacks on the sea islands, advisors teach families how to legally divide land among children to spread the tax burden wider.

Walter Mack works at Penn School as an agricultural adviser. He helps families make a profit from their farms so that they are eligible for commercial farm tax rates. By planting such ``nontraditional'' crops as broccoli, raspberries, and kiwi fruit, farmers can make money from their 10- to 15-acre plots by selling to tourists, he believes.

Mr. Mack is also exploring innovative approaches to development. ``Right now more people are interested in selling than any other alternative. But we're trying to suggest leasing or profit sharing'' of land.

To many whose families have lived here since before living memory, the specter of a changed St. Helena seems hardly possible. At midday the silence and serenity are so complete that the cry of gulls seems to carry forever across the plowed brown fields. In the mossy depths of the forest the sun stands still.

``St. Helena is fine. Can't be no better,'' says Lucile Brown, looking with satisfaction at her great-grandchildren playing in the yard. Islanders like Mrs. Brown remember the lessons of history. Rising to her feet, her voice ringing with conviction, Brown declares, ``It's important to have your own.''